1. Field of the Invention
The present invention relates to the field of cooling, carbonation and dispensing systems. More specifically, the invention relates to a system used for maintaining temperature and carbonation of a liquid, such as beer, and dispensing that liquid from a keg. Although much of the following discussion is directed towards beer as the liquid, those skilled in the art will understand that such a system as that described herein could be used in conjunction with any liquid that is stored inside a keg (pressurized liquid holding vessel).
2. General Background and State of the Art
Beer brewers and beer drinkers generally know that in order to have the best tasting beer as crafted by a brewmaster, they would drink the beer at the brewery directly from the fermenting or lagering (aging) tank. Because beer is extremely sensitive to heat and oxygen, most bottled or canned beer, in order to have a reasonable shelf life, is pasteurized (rapidly heated, then cooled). The pasteurization process inhibits the flavor dynamic and changes the composition of the beer.
Draught beer (keg beer) produced in North America is almost always unpasteurized and retains more fresh beer flavor than beer from bottles or cans. The taste of the beer from the keg, if the keg is handled and maintained properly, can approximate the taste of the beer that can be obtained at the brewery, fresh from the lagering tank.
U.S. domestic draught beer (keg beer) is almost always unpasteurized and retains more fresh beer flavor than beer from bottles or cans. The taste of the beer from the keg, if the keg is handled and maintained properly, can approximate the taste of the beer that can be obtained directly from the lagering tanks at the brewery. In beer markets outside of North America, lack of consistent and effective refrigeration throughout the brewer-to-consumer supply chains, necessitates that the brewer pasteurize draught beer in order to prevent spoilage (for unpasteurized draught beer, spoilage begins at temperatures greater than 45° F.).
Two of the primary factors that affect the composition and taste of draught beer are temperature and carbon dioxide (CO2) gas. The ideal values of these two factors vary between different types and brands of beer, and the balance between these two factors is vitally important in maintaining the best possible taste in draught beer. Temperature affects the taste of draught beer (both unpasteurized and pasteurized), the ability to dispense the draught beer, and the useful life of the beer in the keg. If draught beer is not pasteurized, it must always be kept cold (below 42 and 44° F.) or it will spoil. Ideally, draught beer should be maintained at a constant temperature of approximately 36-38 F as to provide flavorful beer for up to fifty days. Additionally, both unpasteurized and pasteurized draught beer will not dispense in a consumable manner, when passing through a draught beer dispensing system and out a beer faucet into a beer-clean glass, at temperatures greater than 45 F.
CO2 is created naturally during the fermenting process of beer. Further along in the brewing process, additional CO2 is infused into the beer by the brewer. Carbon dioxide is nonflammable, non-toxic, colorless, odorless, and exists in three different states: gas, liquid, or solid. As a gas, CO2 is 1.5 times heavier than air. CO2, in its solid form, is commonly called “dry ice.” CO2, in liquid or gaseous form, is water soluble and dissolves easily in beer. The amount of the gas dissolved into a particular beer is measured in CO2 volumes. For example, if one liter of beer is carbonated to 2.5 volumes, there are 2.5 liters of CO2 dissolved into the beer. CO2 gas is odorless with no detectable flavor, but as it expands out of the beer (bubbles and foams), it does release aromas and flavor characteristics of the beer, affecting the flavor. When a brewer produces a beer, he takes diligent care to control the carbonation level (CO2 content) in a way to bring out the preferred flavors and aromas, as to affect the flavor in a controlled way.
Pressurized CO2 serves a number of functions for kegged beer. CO2 is pumped into the keg to maintain the proper level of balance of CO2 in the beer and it also serves to prevent air (which contains oxygen that promotes bacteria growth) from contacting the beer, which can spoil the composition and taste of the beer. CO2 is also utilized as a pressure source to force the beer out of the keg while maintaining the proper carbonation volume levels of the beer. Currently, outside of Europe and North America, the quality of CO2 gas used for dispensing beer is not always of Food or Beverage Grade. Quality of CO2 gas is region dependant.
Pressure, maintained in pounds per square inch gauge, is defined as the force at which the gaseous CO2 enters the head-space of a keg, pushing on the beer. As the pressure increases, the gas molecules hit the beer with more force and dissolve into the beer more easily. As the pressure decreases, the gas molecules do not dissolve in the beer as easily and CO2 gas can escape from the beer. Excess pressure increases the carbonation level, while inadequate pressure decreases the carbonation level. The right amount of pressure applied to beer inside a keg is needed to maintain the proper or optimal carbonation level of the beer as well as to push the beer through the dispensing system.
The temperature of the beer affects the amount of pressure needed in the keg to control the optimal carbonation level. As the temperature of the beer increases, CO2 expands and the gas bubbles will come out of the beer. As the temperature of the beer decreases, CO2 dissolves more easily into the beer. Generally, a two-degree Fahrenheit increase in beer temperature requires a one pound increase in pressure to maintain optimal carbonation equilibrium, while a two-degree Fahrenheit decrease in beer temperature requires a one pound decrease in pressure to maintain optimal carbonation equilibrium as per the brewer-designed carbonation levels.
It is vitally important to keep the carbonation level of draft beer at the proper (or optimal) brewer-designed carbonation levels. Too little carbonation (low pressure) leads to flat beer. Too high of a carbonation level (high pressure) leads to off-taste problems as well as foaming/dispensing issues.
Typically, a keg of beer served at a private party is stored in a large bucket filled with water and wet ice (as opposed to dry ice) and is dispensed by using pressurized air via a hand-operated pump. Since the beer, in this example, is generally consumed over a relatively short period of time (less than 24 hours), the intent at such an event is to keep the beer cold and to keep sufficient pressure applied to the beer keg so that it may be dispensed. Adding air to draught beer, however, causes the beer to go off-taste due to oxidation, limiting optimal flavor for the duration of the keg. For that reason, often times a high-pressure carbon dioxide supply (CO2 cylinder or CO2 bottle) provides the pressure, via a pressure regulator attached to the carbon dioxide supply, to force the beer out of the keg.
A number of problems are associated with dispensing beer or other kegged liquids in the manner just described. First, there is the presence of a gas trapped under high-pressure in a pressurized container. If the container somehow becomes damaged and the highly-pressurized carbon dioxide gas leaks, there is the potential for injury. Also, the beer or other liquid in the keg will likely spoil because of inadequate pressure. There exists the likelihood that the user may not install and maintain the carbon dioxide system properly, which can quickly make the beer lose its flavor and to make dispensing the beer difficult. Once the pressurized container of gas is empty, it must be immediately refilled from a highly-pressurized liquid CO2 source, or replaced by another pre-filled highly-pressurized vessel. There is also a quality issue in that refilling a small highly-pressurized vessel over time allows for the possibility of air, moisture, dirt, insects or other contaminants to collect on the fittings and/or in the vessel (CO2 cylinder) thereby introducing contaminants into the beer and causing the beer to go off-taste.
Some contaminants, in the form of microorganisms, are not easily cleansed and removed from hoses and from inside the vessel. These microorganisms may cause disease or illness to consumers. One major beverage distributor, Anheuser-Busch, requires U.S.-located users of its products to install a CO2 filter between the CO2 cylinder and the keg to filter out dirt and microorganisms before the CO2 stored in the CO2 cylinder reaches the keg.
In addition, there is the added cost associated with requiring the highly-pressurized container to meet Department of Transportation (DOT) standards. Therefore, DOT high-pressure vessel transportation regulations and restrictions apply to these pressurized vessels (CO2 cylinders) as well.
Another problem associated with dispensing beer in the example just described is that the wet ice bath in which the keg is placed may, depending on the surrounding conditions, melt quickly and reduce the ability to keep the beer cold. This can be especially problematic on hot days. The host or vendor must keep a large supply of wet ice on hand and be alert to replenish the supply of wet ice in the bath and deal with the accumulation of additional water from melting wet ice over time. In some situations, the host or vendor will be inconvenienced by having to make a trip to a store to purchase more wet ice. This difficult situation can be multiplied several times over when liquid from numerous kegs is being dispensed at once, which occurs during outdoor festivals or gatherings.
There thus exists a need for a system for maintaining optimal temperature and proper carbonation as well as dispensing of a liquid, such as beer, that is stored in a keg that does not require the presence of a separate highly-pressurized gas container (commonly called a CO2 cylinder or CO2 bottle) and reduces the need to constantly replenish the supply of wet ice. This system must keep the liquid or beer chilled, optimally carbonated, and under sufficient pressure to dispense the liquid with minimal dispensing issues while maintaining optimal flavor.